Automatic spark advance for magnetos



G..J. SHAW AUTOMATIC SPARK ADVANCE FOR MAGNETOS I June 29, 1965 2Sheets-Sheet 1 Filed Sept. 1. 1960 ,2, x M m/ INVENTOR. eezua J Jun wArraeve'x June 29, 1965 G. J. SHAW AUTOMATIC SPARK ADVANCE FOR MAGNETOSFiled Sept. 1. 1960 2 Sheets-Sheet 2 2a .aa 40 14/4 INVENTOR 615K440JHAM/ MMJ$ A TTORNEY United States Patent 3,192,439 AUTOMATIC SPARKADVANCE FOR MAGNETOS Gerald J. Shaw, Lamar, Mo., assignor to OutboardMarine Corporation, Waukegan, 111., a corporation of Delaware FiledSept. 1, 1960, Ser. No. 53,510 12 Claims. (Cl. 315218) This inventionrelates to an automatic spark advance for magnetos.

The invention is exemplified by conventional illustrations of parts of aflywheel magneto. Because maximum spark intensity is achieved if theprimary circuit of the spark coil is opened when the coil is threaded byflux changing at maximum rate, it is routine to advance or retard thearmature upon which the coil is wound coincidentally with the advance orretard of the breaker cam follower in order to maintain the desiredrelationship. However, the present invention takes advantage of the factthat in a flywheel magneto having a so-called E armature, separate peaksof rate of flux change are built up as the poles of the permanent magnetpass the several poles of the armature. The highest peak occurs, ofcourse, when the direction of flux flow is reversing in the central legupon which the coils are wound. However, there is a lesser peak whichoccurs as the poles of the flywheel magnet first come into registry withone of the side legs and the center leg of the armature, thus initiatingflux rise through the coils.

By an arrangement such that the breaker cam is advanced with respect tothe breaker cam follower for a distance approximately equal to theangular spacing between the points at which these two peaks occur, Ihave achieved a spark advance which does not involve any movement of theE armature or breaker plate, the cam alone being shifted through anangle such that the opening of the primary circuit is shifted from lowspeed syn chronism with the maximum peak rate of flux change, to highspeed synchronism with the lesser but adequate peak of flux buildup,thus giving an ignition spark intensity which is far above average atlow speeds (for starting) and is entirely adequate for proper ignitionat high speeds.

In the drawings:

FIG. 1 is a diagrammatic view showing the relation between the flywheelmagnet and the armature at high engine speeds the magneto shaft beingshown in section approximately on the line 11 of FIG. 6.

FIG. 2 is a view showing the relationship between the breaker cam andcam follower at high speeds, when the flywheel and armature are in therelative positions of FIG. 1, FIG. 2 being taken approximately in theplane shown by the line 22 in FIG. 6.

FIG. 3 is a view similar to FIG. 1 showing the relationship between theflywheel magnet and the armature at starting speeds.

FIG. 4 is a view similar to FIG. 2 showing the relation between thebreaker cam and cam follower at starting speeds, portions of the cambeing broken away to the level of the notches provided in its lowermargin.

FIG. 5 is a graph in which spark coil output is plotted against shaftr.p.m.

FIG. 6 is a diagrammatic view of the shaft and cam and operating weightin side elevation.

FIG. 7 is a view similar to FIG. 6 showing the cam and weight and springand guide pin in relatively separated positions in side elevation.

The shaft shown at 8 would normally be an extension of the enginecrankshaft tapered at 9 to receive the magneto flywheel 10 in whichthere is incorporated a magnet having polar shoes at 16 and 17. Thedesignation of the poles by reference characters N and S is arbitraryand merely by way of example.

In accordance with conventional practice, the polar shoes 16 and 17 havesurfaces at 18 and 19 which are of uniform radius for rotation inimmediate proximity to the three legs of the conventionally laminated(lamination not shown) three legged armature 20. As shown by the arrow21 in FIG. 1 and FIG. 3, the assumed direction of rotation of theflywheel is clockwise. The surface 19 of the S pole 17 first comes intoregistry with the end leg 23 of armature 20, subsequently registeringwith the center leg 24 upon which the coils 25 are wound and finallycoming into registry with the end leg 26. The primary and secondary arenormally connected as diagrammatically shown in FIG. 1.

The first substantial buildup of flux in the E armature 20 occurs in theposition of the parts shown in FIG. 1, the flux flowing from the N poleoutwardly through the leg 23 of the armature and back through the centerleg 24 to the S pole as indicated by the arrows 27 and 28 in FIG. 1.

During continued rotation of the flywheel 10, the surface 18 of thenorth polar shoe 16 then comes into registry with the center leg 24while the surface 19 of the south polar shoe 17 comes into registry withthe leg 26. As this occurs, there is a reversal of flux in the centerleg 24 which threads the coils 25. In the FIG. 1 position of the parts,the flux threading the coil from north to south was passing inwardlythrough the center leg 24 as shown by the arrow 28. In the FIG. 3position of the parts, the flux threading the center leg 24 through thecoils 25 from north to south is passing outwardly through the coils asshown by the arrow 29 and is returned through leg 26 as shown by arrow30.

The breaker is generally conventional, comprising a grounded contact 32which, although mounted on the usual spring 33 is relatively fixed.Movable to and from the contact 32 is the movable contact 35 seriesconnected with the primary coil and carried by spring 36, upon which ismounted the cam follower 37.

The cam 38 which operates the follower 37 to open and close the breakercontacts or points 32 and 35 is illustrated as a sleeve encircling themangeto shaft 8 and oscillatable with respect thereto. It is confined bya split ring 39. The camming surface comprises a flat 40 which iscentrally reduced in radius sufiiciently to permit the contacts to closeas shown in FIG. 4. When the flat 40 is not in registry with thefollower 37, the cam opens the coil circuit through contacts 32 and 35.

The cam may conveniently rest on a sheet metal slide 41 which carriesthe flyweight 42, the weight being almost wholly at one side of the axisof shaft 8. Both the sheet metal slide 41 and the flyweight 42 are cutaway to encircle the shaft 8. An inwardly projecting lug of theflyweight at 43 engages in a radial notch or opening 44 in the camsleeve 38 so that the transverse reciprocation of the cam sleeve inresponse to centrifugal action of the flyweight in one direction and theconverse bias of the spring in the opposite direction will communicaterotative movement to the cam sleeve respecting shaft 8.

The flyweight is socketed at 44 to receive a pin 45 that extendsdiametrically through shaft 8 and serves as a guide for the compressionspring 46. The reduced extremity 47 of the pin 45 is seated in a downturned lug 48 of the slide 41. The bias of spring 46 normally maintainsthe slide 41 and flyweight 42 in the retracted position shown in FIG. 4.At some given speed determined by design, and here exemplified by anassumed shaft speed of about 500 rpm, the flyweight and slide will movefrom the position of FIG. 4 to the position of FIG. 2 against the biasof spring 46, thereby compressing the spring and rotatively advancingthe cam sleeve 38 in the direction of shaft rotation to advance thespark. That is to say, the opening and closing of the contact points 32and 35 will occur earlier in the rotation of the shaft at high speedsthan at low speeds.

Asthe speed of shaft 8 decreases below the assumed rate .of 500 r.p.m.,the bias of spring 46 will overcome the centrifugal force of fiyweight42 to retract the slide to the position of FIG. 4, therebyretarding thespark. As a convenient means of defining the two positions of the camsleeve 38 with respect to shaft 8, the cam sleeve may conveniently beprovided with notches 450 and 451 on a diameter substantially at rightangles to the notch 44. The notches 4'54 and 451 straddle the'pin 45,the notch 450 also accommodating a compression spring 46 as shown inFIG. 4. In the retracted position of the cam shown in FIG. 4, theposition thereof is defined by engagement of the pin with that portionof the cam which is at the left of notch 45% and at the right of notch451. In the advanced position of FIG. 2, the pin 45 and spring 46 areengaged by portions of the cam which are at the left of notch 4'51 andat the right of notch 45%.

In the FIG. graph, thecurve 48 shows a typical relationship between thekv. output of the magneto with an open circuit in a conventional magnetohaving no spark advance. The curve generically designated by referencecharacter 5% shows the kv. open circuit output of a, magneto made inaccordance with the present invention. It will be observed that whereasthe standard magneto has an output of only about nine kv. at 100 rpm.(the assumed figure is arbitrary but fairly represents the situation),the magneto of the present invention under like conditions has an outputof thirteen kv., or an increase of over forty percent.

The curve 50 shows that the magneto of the'present invention not onlymaintains but actually increases its advantage over curve 43 at allspeeds used in starting and in low speed operation. By the time theadvance occurs at the assumed speed of 500 r.p,m., the kv. output isample, even though the breaker is now operating at a relatively lowerpeak in rate of change of the flux threading the coils. Because of thischange in peak, there will be a sharp drop in the portion 51 of curve5t) but the kv. output will still be considerably in excess of thatwhich was available for starting. During continued increase in r.p.m.,the kv. output will continue to build up as shown by the portion 52 ofcurve 50.

It will, of course, be clear that the purpose in advancing the spark isto assure better combustion of the fuel at high speed. It isconventional in both four-cycle and two-cycle engines to advance thespark for high speed operation. However, the apparatus employed for aspark advance in conventional magnetos and other timers involvesshifting of the position of the breaker points, an arrangement madeunnecessary by the present device which takes advantage of the fact thata magneto has more than one peak at which breaker point operation eitherin a closing or an opening direction will assure adequate ignitioncurrent, particularly if the higher peak is used for starting and therelatively lower peak for high speed operation in accordance with thepresent disclosure.

In the specific embodiment disclosed, for the purposes of exemplifyingthe invention, the cam has an oscillatory movement of approximatelynineteen degrees with reference to the magneto shaft to effect anadvance of the spark from approximately eleven degrees before top deadcenter to approximately thirty degrees before top dead center, thisadvance being achieved with simpler and less expensive moving parts thanare normally required for ignition spark advance and retard.

In the low speed operation the breaker interrupts the primary circuit atthe time of reversal of flux threading the coil in the center leg of thelaminated armature 24); in high speed operation, the breaker opens theprimary circuit at the time of flux introduction into the center leg andthe coil.

I claim:

1. In a magneto having a coil and means including relatively movablemagnet and armature parts for developing flux change in said coil at aplurality of points in the course of such movement, the combination witha breaker including a shaft, contact points having a cam follower fortheir operation, and a cam on the shaft, of means for automaticallyshifting in a direction angularly of the shaft the point of cooperativeactuation of the cam follower by the earn from a first position in whichflux change is developed in said coil to a second position in which fluxchange is developed in said coil, said shifting means comprising an offcenter weight provided with a slide guiding it for movementdiametrically of the shaft, the shaft having a transverse bore, a pinextending through the bore and seated in the weight at one end andhaving a connection with the slide at its opposite end, said weighthaving a motion transmitting connection to the cam and the cam beingmounted rotatably on the shaft for movement with respect to the shaft inthe course of its rotation with the shaft, and a spring biasing saidweight toward the shaft axis, spring encircling the pin and having seatson the shaft and the slide.

2. In a magneto, the combination of a shaft, a magnet carried therebyand provided with polar shoes angularly spaced in the direction of shaftrotation, a three-legged armature having its legs spaced proximate thepath of shoe rotation and provided with coil means wound upon its centerleg to be threaded by flux developed in the armature and having rate offlux change peaks at a plurality of points as said polar shoes rotatepast the legs of the armature, a breaker connected in series with thecoil means, said breaker including relatively separable contact points,and means for actuating said points for separation with respect to eachother including means for automatically shifting with respect to saidshaft the timing'of actuation of said points from registry with one ofsaid peaks to registry with another thereof.

3. In a magneto, the combination with a shaft and a magnet carriedthereby and provided with polar shoes angularly spaced in the directionof shaft rotation, of a three-legged armature having its legs spacedproximate the path of shoe rotation and provided with coil means woundupon its center leg to be threaded by flux developed in the armature andhaving rate of flux change peaks at a plurality of pointsas said polarshoes rotate past the legs of the armature, a breaker connected inseries with the coil means and including relatively separable contactpoints, and means for actuating said points for separation with respectto each other including a cam mounted on the shaft for angularoscillation relative thereto, a cam follower connected with one of thebreaker points and with which the cam interacts, and means forautomatically shifting with respect to said shaft the timing ofactuation of said points for registry with one of the said peaks toregistry with another thereof, said shifting means comprising a weighthaving its net mass off center respecting the shaft and provided withmeans biasing it toward the shaft, means guiding said weight forcentrifugally operable movement of its net mass away from the shaft inopposition to said bias at a predetermined shaft speed, said guidingmeans comprising a slide upon which said weight is mounted for movementdiametrically of the shaft, the weight and cam respectively havinginterengaged motion transmitting parts, and means on the shaft fordirecting said slide movement, whereby movement of the weight and slideeffects cam oscillation respecting the shaft for a'distance angularlyequivalent to the distance of shaft rotation between the points at whichsaid peaks occur, the means directing the slide comprising a pinextending through a bore with which the shaft is provided, the pin beingconnected at its ends with the slide, said biasing means comprising aspring encircling the pin and having a seat at one end against the shaftand a seat at its other end against the slide.

4. The device .of claim 3 in which the interengaging 55 parts of theweight and the cam comprise a finger on the Weight, the cam having anotch in which the finger is engaged.-

5. The device of claim 3 in which the cam has notched portionsstraddling the pin and comprising surfaces spaced at said notchedportions sufficiently widely to accommodate oscillatory movement of thecam respecting the pin and to define the extent of such movement.

6. In a magneto, the combination of a rotatable shaft, an E-shapedarmature including a pair of end legs and a center leg, and coil meanswound on the center leg of said armature, a sole magnet carried by saidshaft for travel relative to said armature in response to rotation ofsaid shaft, said travel of said magnet relative to said armatureproducing a first peak condition of substantial flux change in saidarmature incident to registry of said magnet With the central leg andone of said pair of end legs, and a second peak condition of substantialfiuxchange in said armature incident to registry of said magnet withsaid center leg and the other of said pair of end legs, a cam carried bysaid shaft for rotation by said shaft and for oscillation relative tosaid shaft, a. breaker including separable points, said points beingoperated by action of said cam in response to rotation of said shaft,and means for effecting oscillation of said cam relative to said shaftbetween first and second cam positions respectively operable to opensaid points during said first and second peak conditions of substantialflux change.

7. A magneto in accordance with claim.6 wherein one of said flux changeconditions is of greater ma nitude than the other and occurs when saidmagnet is in angularly spaced relation in the direction of rotation ofsaid shaft from its position during the condition of lesser flux change,and

said means for effecting oscillation of said cam is perable to effectopening of said points during the occurrence of said greater flux changecondition when said shaft is rotating at relatively low speeds and isoperable to effect opening of said pointsduring the occurrence of saidlesser flux change condition when said shaft is rotating at relativelyhigh speeds.

8. In a magneto, means including relatively movable magnet and armatureparts for developing at least two peak conditions of rate of flux changein response to relative rotation between said magnet and said armatureparts, an ignition circuit including a sparkplug, and means forselectively operating said ignition circuit to produce a spark at saidplug attimes corresponding to the occurrence of said peak conditions ofrate of flux change.

9. In a magneto, the combination of a shaft, a magnet carrie'd'therebyand provided with polar shoes angularly spaced in the direction of shaftrotation, a three-legged armature having two legs spaced proximate tothe path of shoe rotation and provided with coil means wound upon itscenter leg to be threaded by flux developed in the armature and havingrate of flux change peaks at a plurality of points as said polar shoesrotate past the legs of said armature, a breaker connected inseries withsaid coil means, said breaker including relatively separable contactpoints and means for actuating said points for operation with respect toeach other including a cam on said shaft mounted for angular oscillationwith respect to said shaft, a cam follower connected with one of saidbreaker points and with which said cam interacts, and means forautomatically shifting with respect to said shaft the timing ofactuation of said points from registry with one of said peaks toregistry with another of said peaks, said shifting means comprising aweight having its net mass off center with respect to said shaft andprovided with means biasing it toward said shaft, means guiding saidweight for centrifugally operative movement of its net mass away fromsaid shaft in opposition to said bias at a predetermined shaft speed,said guiding means comprising a slide upon which said weight is mountedfor movement diametrically of said shaft, said shaft having means fordirecting said slide movement, and a motion transmitting connection withsaid Weight for effecting angular cam displacement with respect to saidshaft for a distance angularly equivalent to the distance of shaftrotation between the points at which said peaks occur, said motiontransmitting connection including interengag ed parts whereby themovement of said weight with said slide effects cam oscillation withrespect to said shaft.

10. An ignition device including a sole magnet having a pair of polefaces of opposite polarity, an armature including, in series, first,second, and third legs and a primary winding on said second leg, meansmounting said magnet and said armature for relative rotative movementtherebetween, circuit breaker means connected to said primary winding,and means for selectively operating said circuit breaker means forproduction of a spark by a spark plug when said magnet is in a firstposition inducing fiux along a path through said first and second legsand when said magnet is in a second position inducing flux along a paththrough said second and third legs.

11. An ignition device including a sole magnet having a pair of polefaces of opposite polarity, an armature including, in series, first,second, and third legs and a primary winding on said second leg, meansmounting said magnet and said armature for relative rotative movementtherebetween to establish first and second successively occurring fiuxpaths in said second leg and to successively induce flux flow along saidfirst and second paths, said first fiux path extending in said first andsecond legs and said second flux path extending in said second and thirdlegs, circuit breaker means connected to said primary winding, and meansfor selectively operating said circuit breaker means for production of aspark by a spark plug when said magnet is in a first position inducingflux flow along said first path and when said magnet is in a secondposition inducing flux flow along said second path.

12. An ignition device including a sole magnet having a pair of polefaces of opposite polarity, an armature including, in series, first,second, and third legs and a primary winding on said second leg, meansmounting said magnet and said armature for relative rotative movementtherebetween for successively inducing flux in said second leg alongsuccessively occurring first and second paths, said first path includingsaid first and second legs and generally excluding said third leg, andsaid second path including said second and third legs and generallyexcluding said first leg, circuit breaker means connected to saidprimary winding, and means for selectively operating said circuitbreaker means for production of a spark by a spark plug when said magnetis in a first position inducing flux fiow alongsaid first path and whensaid magnet is in a second position inducing flux flow along said secondpath.

References Cited by the Examiner UNITED STATES PATENTS 2,806,156 9/57Phelon. 2,843,769 7/58 McGrevy 310-153 X 2,982,805 5/61 Glenday.3,105,481 10/63 Hoiby et al. 310- X FOREIGN PATENTS 601,264 5/48 GreatBritain. 947,659 1/49 France.

MILTON O. HIRSHFIELD, Primary Examiner. ORIS, L. RADER, DAVID X. SLINEY,Examiners.

8. IN A MAGNETO, MEANS INCLUDING RELATIVELY MOVABLE MAGNET AND ARMATUREPARTS FOR DEVLOPING AT LEAST TWO PEAK CONDITIONS OF RATE OF FLUX CHANGEIN RESPONSE TO RELATIVE ROTATION BETWEEN SAID MAGNET AND SAID ARMATUREPARTS, AN IGNITION CIRCUIT INCLUDING A SPARK PLUG, AND MEANS FORSELECTIVELY OPERATING SAID IGNITION CIRCUIT TO PRODUCE A SPARK AT SAIDPLUG AT TIMES CORRESPONDING TO THE OCCURRENCE OF SAID PEAK CONDITIONS OFRATE OF FLUX CHANGE.